What does this do

[Takhisis]

OK, would this work? I create a wwII scenario with the regular civs including germany and finland. with finland as a nonplayable civ. I then reassign all finland to the german player, essentially making finland a playable ally of the german player. Would that work?

No, they'd all be one and the same. If you want them to be allies but still be separate civs you have to set a Locked Alliance.